1. Field of the Invention
The present invention relates to a method for aligning an object to be processed with a predetermined target article and a system for carrying out the same.
It is well known that a stepping projection aligner (a so-called xe2x80x9cstepperxe2x80x9d) has been used in general for carrying out the photolithography treatment of a semiconductor wafer (simply called a xe2x80x9cwaferxe2x80x9d hereinafter) in the manufacturing process of semiconductor devices. In the photolithography treatment of the wafer by using such a stepper, the most important point is to align the wafer mounted on a stage (called a stage chuck or a reticle stage) with a reticle pattern which has been set up in advance in a predetermined position of the stepper.
2. Prior Art
The prior art process for aligning the wafer with a target article has been carried out in general in the following manner.
The wafer conveyed to the stepper is first preliminarily positioned by using a pre-aligner of the stepper such that the direction of the wafer, more particularly, the direction of a alignment mark pattern formed in advance on the wafer surface, coincides with the direction of the reticle pattern. The wafer preliminarily positioned by the pre-aligner is further conveyed to a stage and is then finally aligned with the reticle pattern by means of an alignment optical system. As described above, the wafer includes a plurality of alignment marks formed in advance on the surface of the wafer for the purpose of alignment, and the alignment by the alignment optical system is carried out by detecting the waveform of an alignment light reflected by the alignment marks, which are irradiated by the alignment light (laser rays). After detecting the waveforms of the reflected alignment light with respect to all the alignment marks, a positional correction factor with respect to the wafer position is calculated, based on the detection of the reflected waveforms. The stage carrying the wafer is then moved in the necessary direction to correct the wafer position based on the result of the above calculation on the positional correction factor, and finally, the exposure of the wafer to the reticle pattern light is carried out to copy the reticle pattern thereto.
However, the method for aligning the wafer with the reticle pattern as described above has some problems, especially a reduction in the accuracy of the alignment that is achieved. This alignment accuracy reduction is mainly caused by the following reasons. The first reason relates to an incomplete optical adjustment, which may cause a certain difference between the optical path of the incident alignment light and that of the reflected one. The second relates to the use of laser rays as the alignment light. In this case, if the optical path of the incident laser rays coincides with that of the reflected one, interference may be caused there between. In order to avoid this, some type of optical adjustment is required with respect to the optical paths of the incident and reflected alignment light rays, for instance, making a certain angle between the incident alignment light entering the alignment optical system and the reflected one coming out therefrom. The third reason relates to an incomplete positional adjustment between parts constituting the alignment optical system. Due to such reasons as described above, some deformation might be caused in the waveform of the reflected alignment light, thereby causing a reduction in the accuracy of the alignment.
The present invention has been made in view of various problems as described above in connection with the prior art method for aligning the object to be processed, and its object is to provide a novel and improved method and system for aligning the object to be processed, having a much enhanced alignment accuracy comparing with the prior art method and system.
In order to solve the problems as described above, according to the present invention, there is provided a method for aligning an object to be processed with a predetermined target article. This method is executed by a system which includes a pre-aligner for positioning the object before conveying it into a processing area, and a stage for supporting the object from the underside thereof, and is characterized by the following processes, that is, the first process for conveying the object to the pre-aligner to mount it thereon, operating the pre-aligner to rotate the object about the center thereof by +90 degrees with respect to the reference direction, and positioning the object in such rotated state; the second process for conveying said object to the stage to mount it thereon and detecting the positional data with respect to the object in such rotated state; the third process for again conveying the object to the pre-aligner to mount it thereon, operating the pre-aligner to rotate the object by xe2x88x9290 degrees with respect to the reference direction, and positioning the object in such a rotated state; the fourth process for again conveying said object to the stage to mount it thereon and detecting the positional data with respect to the object in such a rotated state; the fifth process for calculating the positional correction factor for the object position by making use of the detection results attained through the second and fourth processes; and the sixth process for finally conveying the object to the pre-aligner to mount it thereon, and operating the pre-aligner to rotate the object to direct it to the reference direction.
According to the present invention, there is provided another method for aligning an object to be processed with a predetermined target article. This method is executed by a system which also includes a pre-aligner for positioning the object before conveying it into a processing area, and a stage for supporting the object from the underside thereof, and is characterized by the following processes, that is, the first process for conveying the object to the pre-aligner to mount it thereon, operating the pre-aligner to rotate the object about the center thereof by 180 degrees with respect to the reference direction, and positioning the object in such a rotated state; the second process for conveying said object to the stage to mount it thereon and detecting the positional data with respect to the object in such rotated state; the third process for again conveying the object to the pre-aligner to mount it thereon, operating the pre-aligner to rotate the object to direct it to the reference direction, and positioning the object in such rotated state; the fourth process for again conveying the object to the stage to mount it thereon and detecting the positional data with respect to the object directed to the reference direction; and the fifth process for calculating the positional correction factor for the object position by making use of the detection results attained through the second and fourth processes.
Furthermore, according to the present invention, there is provided still another method for aligning an object to be processed with a predetermined target article. This method is executed by a system which also includes a pre-aligner for positioning the object before conveying it into a processing area, and a stage for supporting the object from the underside thereof, and is characterized by the following processes, that is, the first process for conveying the object to the pre-aligner to mount it thereon, operating the pre-aligner to rotate the object by +90 degrees with respect to the reference direction, and positioning the object in such a rotated state; the second process for conveying the object to the stage to mount it thereon and detecting the positional data with respect to the object in such rotated state; the third process for operating the stage to rotate the object mounted thereon by xe2x88x92180 degrees and then detecting the positional data of the object in such a state that the object is substantially rotated byxe2x88x9290 degrees with respect to the reference direction; the fourth process for calculating the positional correction factor for the object position by making use of the detection results attained through the second and third processes; and the fifth process for again rotating the stage by +90 degrees to direct the object to the reference direction.
Still further, according to the present invention, there is provided still another method for aligning an object to be processed with a predetermined target article. This method is executed by a system which also includes a pre-aligner for positioning the object before conveying it into a processing area, and a stage for supporting the object from the underside thereof, and is characterized by the following processes, that is, the first process for conveying the object to the pre-aligner to mount it thereon, operating the pre-aligner to rotate the object by +180 degrees with respect to the reference direction, and positioning the object in such a rotated state; the second process for conveying said object to the stage to mount it thereon and then detecting the positional data with respect to the object in such rotated state; the third process for operating the stage to rotate the object mounted thereon by xe2x88x92180 degrees and then detecting the positional data of the object in such a state that the object is substantially directed to the reference direction; and the fourth process for calculating the positional correction factor for the object position by making use of the detection results attained through the second and third processes.
Furthermore, in order to solve the problems as described above, according to the present invention, there is provided a system for aligning an object to be processed with a predetermined target article. This system includes a pre-aligner for positioning the object before conveying it into a processing area; and a stage for supporting the object from the thereof, wherein the pre-aligner and/or the stage includes a rotation mechanism capable of rotating object.